1. Technical Field
The present invention relates to a stacked-type image pickup device having a photoelectric conversion layer on the upper side of a substrate and an image pickup apparatus including the image pickup device.
2. Related Art
In a single-plate image pickup device that is mainly represented by a CCD image sensor or a CMOS image sensor, color signals corresponding to color filters are output from pixel portions through three or four types of mosaic-shaped color filters that are disposed on the upper side of the arrangement of the pixel portions (photo diodes) that perform photoelectric conversion. The color signals output from the single-plate image pickup device are processed so as to generate color image data. However, when the mosaic-shape filters are filters of primary colors, about ⅔ of incident light is absorbed by the color filters. Accordingly, in a single-plate image pickup device in which the mosaic-shaped color filters are disposed, the light use efficiency in each pixel portion is low, and it is difficult to raise the sensitivity. In addition, since only a color signal of one color is acquired in each pixel portion, it is difficult to increase the resolution, and a false color is generated.
Thus, in order to address such cases, for example, an image pickup device disclosed in JP-T-2002-513145 is developed. According to this image pickup device, by arranging three-folded wells (photo diodes) that detect an optical signal within a silicon substrate, signals (having peak values at the wavelengths of blue, green, and red on the surface) having different spectral sensitivities in accordance with a difference in the depths of the silicon substrate may be acquired. According to this image pickup device, the resolution is good, and the light use efficiency is improved. However, the separation of spectral sensitivity characteristics of RGB output signals is not sufficient, and color reproducibility deteriorates. In addition, in order to acquire real RGB signals, addition and subtraction of the output signals are performed. However, the S/N deteriorates due to the addition or the subtraction.
Accordingly, as in JP-T-2002-502120 and JP-A-2002-83946, image pickup devices that may separate the spectral sensitivity characteristics of the RGB output signals well are researched and developed. In such image pickup devices, each pixel portion has a structure in which photoelectric conversion layers sequentially generating signal electric charge for light of B, G, R are sequentially stacked, for example, from the light incident side. Then, in each pixel portion, a reading portion that may independently read out a signal corresponding to electric charge generated by light in each photoelectric conversion layer is disposed integrally with the pixel portion. In such an image pickup device, since any color filter is not placed on the upper side of each pixel portion, the use efficiency of visible light may be configured to be almost 100%. In addition, since a structure in which three photoelectric conversion layers are stacked is used, color signals of three colors of R, G, and B may be acquired in each pixel portion. Furthermore, the spectral sensitivity characteristics of the three photoelectric conversion layers may be independently selected. Accordingly, separation of the spectral sensitivity characteristics of the RGB output signals is good. As a result, an image having high sensitivity, high resolution (a false color is not visually recognizable), excellent color reproducibility, and good S/N may be acquired.
The inventor of the present invention has found a disadvantage in that unevenness occurs in an image due to the structure in a stacked-type image pickup device as disclosed in JP-T-2002-502120 and JP-A-2002-83946. Hereinafter, the disadvantage will be described with reference to the drawings.
FIG. 61 is a schematic diagram showing the cross-section of a stacked-type image pickup device that is conventionally proposed. The image pickup device shown in FIG. 61 includes a plurality of pixel portions P arranged in a two dimensional shape. Each pixel portion P includes a substrate 1, an insulating layer 2, a photoelectric conversion layer 3, an opposing electrode 4, a pixel electrode 5, a connection portion 6, and a signal reading portion 7. The pixel electrode 5 is disposed on the insulating layer 2 disposed on the substrate 1 and is separated for each pixel portion P. The photoelectric conversion layer 3 is disposed on the pixel electrode 5, and one photoelectric conversion layer 3 that is common to all the pixel portions P is configured. The opposing electrode 4 is disposed on the photoelectric conversion layer 3, and one opposing electrode 4 that is common to all the pixel portions P is configured. The signal reading portion 7 is formed in the substrate 1 and is configured by an MOS circuit or the like. The connection portion 6 is formed from a conductive material that electrically connects the pixel electrode 5 and the signal reading portion 7 to each other. In the pixel portion of the image pickup device, by applying an electric field between the opposing electrode 4 and the pixel electrode 5, the electric charge (electrons or holes) generated in the photoelectric conversion layer 3 moves to the pixel electrode 5. Then, a signal corresponding to the electric charge moved to the pixel electrode 5 is read out by the signal reading portion 7 and is externally output.
FIG. 62 is a diagram of the image pickup device shown in FIG. 61 viewed from the top face. In FIG. 62, the opposing electrode 4 is not shown. As shown in FIG. 62, a plurality of pixel portions P is arranged in a tetragonal lattice shape. The partitioned area of each pixel portion P is a square. The pixel electrode 5 included in each pixel portion P is in the shape of a square that is smaller than the pixel portion P and is disposed in the center of the partitioned area of the pixel portion P. In addition, the pixel electrodes 5 of the pixel portions P, similarly to the pixel portions P, are arranged in a tetragonal lattice shape. Accordingly, the distances between adjacent pixel electrodes 5 are the same in all the pixel portions. In FIG. 62, the pixel electrodes, which are positioned on the outermost side, out of a plurality of the pixel electrodes are denoted by white beta blocks that are not hatched.
When focused on one pixel portion P, there is a gap between the pixel electrode 5 included in the pixel portion P and the end portion of the pixel portion P, and a weak electric field is applied between the gap. Accordingly, electric charge generated in this gap move to the pixel electrode 5 and is converted into a signal. Therefore, as signals output from the pixel portion P, there are not only a signal corresponding to the electric charge generated in the photoelectric conversion layer 3 between the pixel electrode 5 and the opposing electrode 4 but also a signal corresponding to the electric charge generated in this gap.
Regarding the pixel electrode 5 that is hatched in FIG. 62, four sides of the pixel portion P including the pixel electrode 5 are brought into contact with other pixel portions P. Accordingly, there is no electric charge that move to the pixel electrode 5 from the outside of the pixel portion P including the pixel electrode 5. However, regarding the pixel electrode 5 that is not hatched in FIG. 62, one or two out of the four sides of the pixel portion P (the pixel portion P positioned on the outermost periphery) including the pixel portion 5 are not brought into contact with other pixel portions P, and electric charge moves to the pixel electrode 5 from the photoelectric conversion layer 3 that is located on the further outer side of the pixel portion P that is positioned on the outermost periphery.
Accordingly, in the pixel portion P, which is positioned on the outermost periphery, out of the plurality of pixel portions P, the electric charge collected in the pixel electrode 5 is more than the electric charge of the pixel portion P (the pixel portion P including the pixel electrode 5 that is hatched) located on the inner periphery (see FIG. 62). Accordingly, the electric potential of the pixel electrode 5 rises (or drops). Regarding the pixel portions P (the pixel portions P located on the outermost end) located on four corners out of the pixel portions P located on the outermost periphery, other pixel portions P are brought into contact with only two sides of the pixel portions P, and accordingly, particularly the electric potentials thereof rise (or drop). As a result, an image that is based on the signal output from the image pickup device is as shown in FIG. 63.
FIG. 63 is a diagram representing an example of a picked-up image that may be acquired when an image pickup operation is performed at a constant amount of light by using the image pickup device shown in FIGS. 61 and 62. As shown in FIG. 63, in the image picked up at a constant amount of light, pixels, which are located on the outer periphery, corresponding to the pixel portions P located on the outermost periphery are brighter than pixels located, which are located, on the inner periphery, corresponding to the pixel portions P located on the inner periphery, thereby unevenness of the image occurs. Particularly, the pixels, which are located on the outermost end, corresponding to the pixel portions P located on the outermost end are the brightest.
In addition, in the image pickup device shown in FIGS. 61 and 62, by not using signals read out from the pixel portions P located on the outermost periphery as image signals, the unevenness of the image may be considered to be suppressed. However, even when the signals read out from the pixel portions P located on the outermost periphery are not used as image signals, the image quality may deteriorate. The reason is as follows. When the electric potential of the pixel electrode 5 exceeds an ordinary range, electric charge is over flown from the pixel electrode 5, and such electric charge may have influence on the electric potential of the pixel electrode 5 of the pixel portion P located on the inner periphery. As miniaturization advances, the gap between the pixel electrodes 5 becomes narrower, and the deterioration of the image quality due to such a factor is considered to easily occur.
In JP-T-2002-502120 and JP-A-2002-83946, the disadvantage of deterioration of the image quality caused by the structure of such a stacked type image pickup device is not fully touched. In addition, any configuration that may address such a disadvantage is not used.